Pike River victims: 27 of the 29 miners who died at the mine. Photograph: Ho/Reuters

All 29 miners in a southern New Zealand coal mine died within minutes of an initial explosion that rocked the mine in November, an inquest heard today.

The fate of the men had been uncertain for days after the 19 November methane-fuelled blast, because a buildup of poisonous gases prevented rescuers from entering the Pike River mine outside the town of Greymouth. The miners were declared dead only five days later, after a second massive blast that officials said would have killed anyone underground.

The chief coroner, Neil MacLean, said evidence showed the men died from a combination of concussion, burns or hypoxia caused by toxic gases and a lack of oxygen after the initial blast.

MacLean told the inquest at a district courthouse in Greymouth that the men's deaths occurred either at "the immediate time of the large explosion that occurred in the mine or a very short time thereafter".

Earlier this month, officials said they abandoned attempts to recover the men's bodies because the mine is still considered too dangerous and unstable for recovery teams to enter.

Wider issues concerning the cause and possible prevention of the disaster will be covered later by a Royal Commission of Inquiry.

Pike River Coal had been operating for about two years. It sold coking coal to offshore steel producers and was New Zealand's second-biggest coal exporter.

New Zealand's mine sector is generally safe with 181 people killed in the past 114 years. The worst disaster was in March 1896 when 65 miners died in a gas explosion. The Pike River blasts occurred in the same coal seam.